Growth of ternary compounds utilizing solid, liquid and vapor phases

ABSTRACT

This disclosure provides a process for obtaining a ternary compound with a particular composition or with continuous range of compositions utilizing steps of a chemical vapor deposition procedure which cannot normally be obtained directly by chemical vapor deposition itself. Through the chemical vapor deposition procedure, a first layer of GaP is deposited epitaxially onto a crystalline substrate; thereafter a layer of InP is deposited on the first GaP layer; and finally another GaP layer is deposited on the InP layer. The layers have especially good metallurgical contact with each other and are essentially free of imperfections at the interfaces. In accordance with the solid-liquid-solid procedure of the prior art, the sandwich structure obtained via the noted chemical vapor deposition procedure is established at a given temperature above the melting point of the InP layer but below the melting point of the GaP layers and equilibrium of the ensemble is established thereat. Thereafter, the temperature of one of the interfaces between the GaP layers and the InP liquid zone is cooled and the resultant GaxIn1 xP layer growth is initiated. Conveniently, a temperature gradient is imposed on the sandwhich structure ensemble and the growth of the GaxIn1 xP layer continues until the GaP layer at the higher temperature is consumed, or the growth thereof is otherwise terminated.

llnited States Patent 1191 Chicotlra et a1.

1451 Oct. 23, 1973 1 GROWTH OF TERNARY COMPOUNDS UTILIZING SOLID, LIQUID AND VAPOR PHASES I [75] lnventors: Richard J. Chicotka, Mahopac;

Robert C. Taylor, Katonah, both of N.Y.

[73] Assignee: International Business Machines Corporation, Armonk, N.Y.

22 Filed: June 30,1971

21 Appl.No.: 158,314

3,394,390 7/1968 Cheney 148/174 X 3,496,429 2/1970 Robinson 148/175 UX 3,471,324 10/1969 Wilson et al.. 148/175 UX 3,249,473 5/1966 Holonyak 148/175 Primary ExaminerG. T. Ozaki Attorney-Bernard N. Wiener et al.

[57] ABSTRACT This disclosure provides a process for obtaining a ternary compound with a particular composition or with continuous range of compositions utilizing'steps of a chemical vapor deposition procedure which cannot normally be obtained directly by chemical vapor deposition itself. Through the chemical vapor deposition procedure, a first layer of 0a? is deposited epitaxially onto a crystalline substrate; thereafter a layer of InP is deposited on the first GaP layer; and finally another GaP layer is deposited on the lnP layer. The layers have especially good metallurgical contact with each other and are essentially free of imperfections at the interfaces. In accordance with the solid-liquid-solid procedure of the prior art, the sandwich structure obtained via the noted chemical vapor deposition procedure is established at a given temperature above the melting point of the In? layer but below the melting point of the GaP layers and equilibrium of the ensemble is established thereat. Thereafter, the temperature of one of the interfaces between the GaP layers and the In? liquid zone is cooled and the resultant Ga ln- P layer growth is initiated. Conveniently, a temperature gradient is imposed on the sandwhich structure ensemble and the growth of the Ga ln s P layer continues until the Ga? layer at the higher temperature is consumed, or the growth thereof is otherwise terminated.

5 Claims, 6 Drawing Figures PATENTEUHUZS ms 3. 767,472

SHEET 2 BF 3 FIG. 1C

FIG. 2A l ,1 0

SUBSTRATE SINGLE CRYSTAL CVD 4ST LAYER 104 GaP y CVD 2ND LAYER we InP cvn

3RD LAYER N108 GoP GROWTH OF TERNARY COMPOUNDS UTILIZING SOLID, LIQUID AND VAPOR PHASES BACKGROUND OF THE INVENTION In the growth of ternary compounds for Subsequent semiconductor device fabrication, it is very difficult to achieve a constant composition in the device structure because the usual growth process limits the availability of these materials. Heretofore, only the solid-liquidsolid process of copending application Ser. No. 860,316 has been especially suitable for growing ex tended layers of constant composition. Copending ap'- plication Ser. No. 860,316 for Method of Growth of a Mixed Crystal with Controlled Composition by S. E. Blum et al, was filed Sept. 23, 1969, now U.S. Pat. No. 3,628,998, and is commonly assigned. The difficulties associated with the various prior art growth processes have their origin in the fact that most growth processes are inherently non-equilibrium processes. However, these non-equilibrium growth processes are governed to some extent by equilibrium considerations. Illustratively, if a ternary semiconductor compound is to be lit prepared with one volatile species, it is necessary to combine in a crucible both of the non-volatile species and to heat them to some elevated temperature and to react the mixture with the volatile gas species. The resulting liquid is an equilibrium one insofar as the temperature and pressure are fixed for this growth process. However, the resulting solid although initiated as an equilibrium solid, rapidly changes its composition in accordance with the characteristics of the pseudobinary phase diagram or ternary phase diagram which depicts its behavior as-a function of temperature and pressure. Thus, for the directional solidification of a semiconductor melt, it is expected that an ingot will be grown with varying composition along the growth axis. This leads to a crystal with a composition gradient in the direction of growth. For the devices of the semiconductor industry this is not desirable.

It is desirable for semiconductor devices to have a crystal with controlled composition in the growth direction. Prior art methods-for growingsuch crystals with constant composition have been devised but have had a limited application.

Among the materials which have not conveniently been growable by the prior art procedures are the following: the homologous group of mixed llI-Ill-V arsenides, phosphides and antimonides, e.g., Ga ln P, Ga,In ,As, Ga In Sb, ln Al P, ln,A1, As, and In,Al ,,Sb, and some of the extremely reactive compounds such as AlP, As.

OBJECTS OF THE INVENTION It is an object of this invention to provide a method for growth of compounds with more than two components with a particular composition or with a continuous range of compositions, e.g., ternary compound Ga,ln ,P where0 x l.

It is another object of this invention to obtain the foregoing object by growth of a ternary compound through cooperation of a chemical vapor deposition procedure and a solid-liquid-solid growth procedure.

It is another object of this invention to provide the ternary compound Ga In P where O x l by first depositing sequentially layers of GaP, InP and GaP as a three layer structure by a chemical vapor deposition procedure. Thereafter, the ternary compound is caused to grow by raising the temperature of the three layer structure such that the In? layer melts and equilibrium at the melting temperature is established with the adjacent layers of GaP. Thereafter, there is cooling selectively of one of the interfaces between the solid and the liquid such that the ternary compound grows thereat.

SUMMARY OF THE INVENTION layered sandwich structure required for the subsequent solid-liquid-solid growth of the ternary semiconductor. Exemplary advantages of the combined procedures are: the single crystal seed portion of the sandwichstructure may be produced by vapor transport; and the starting binary semiconductor materials and the final ternary material are produced in one apparatus, an example herein is for Ga ln l; the net chemical impurity levels of these starting materials are reduced by using a chemical vapor deposition procedure; and a good metallurgical contact or bond can be obtained between the seed crystal layer and the adjacent layer.

A single crystal GaP seed may be used directly for the seeding of the ternary. Alternatively, an exemplary GaAs substrate is mounted horizontally in a standard vapor transport apparatus containing both Ga and In sources. The temperature thereof is raised to 800C. At this temperature, a single crystal GaP layer is grown on the GaAs substrate either by a Ga-PCl or a GaHCl-PH transport procedure. Illustratively, when the required thickness of the single crystal GaP layer is obtained, reactant flow is stopped and the substrate temperature is lowered to 650C. Thereafter, In? is grown onto the single crystal GaP layer by either of the noted vapor transport procedures with In being used in place of Ga. For solid-liquid-solid growth, the InP layer need not be single crystal. When the desired thickness of InP is obtained, the reactant flow is stopped, the substrate temperature raised again to 800C, and the final layer of Ga? is grown to the desired thickness. Thereafter, vapor growth is terminated with the completion of the GaAsGaPlnPGaP structure. The temperature of the system is then raised above the melting point of InP, i.e., 1070, but maintained below the melting points of GaP, i.e., 1450C, or of GaAs, i.e., 1235C, when used as a substrate, in order to initiate the solid-liquid-solid growth process. A P, atmosphere is maintained in the system by means of PH;, to inhibit the loss of P from the molten InP through decomposition. The melt is maintained at the temperature required to precipitate the desired ternary composition at the seed GaP-melt interface, e.g., for Ga smegmatmperaiarafiC. The required temperature gradient at the seed-melt interface is established by introducing a cooling gas stream into the substrate holder through the holder support rod. As ternary compound precipitation takes place, the position of the temperature gradient can be adjusted readily by increasing the flow of the cooling gas.

The advantages of the layers of Ga In P grown by practice of the principles of this invention will now be additionally discussed. The growth process as described herein is economically feasible at a device production level. Small amounts of GaP and InP are suitable for the operation of this invention since it is desirable to obtain thin layers of the ternary compound Ga In ,P. Most device work is presently being done with thin layers of semiconductor materials. Another important advantage of this invention is that in the growth of thin layers the amount of strain within a thin regrown layer is less than the strain within a thicker regrown layer. In the practice of the noted prior art solid-liquidsolid procedure, the resulting ternary compounds may be highly strained and may be subject to crack fracture. These difficulties of the prior art practice are obviated by the practice of this invention since the layers which are grown thereby are generally thinner than the substrate material and tend to conform to the geometry of the substrate material.

Further, there are other materials which cannot suitably be grown by vapor chemical deposition and an advantageus layer can be obtained by the practice of the principles of this invention which includes a combination of procedures utilizing solid, liquid and vapor phases. Among the materials which have not conveniently been growable by the prior art procedures but are readily grown by practice of this invention are the following: the homologous group of mixed III-III-V arsenides, phosphides and antimonides, e.g., Ga In, P, Ga,In As, Ga ln sb, In Al P, ln Al As and In, Al ,Sb, and some of the extremely reactive compounds such as AlP As The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTIONS OF THE FIGURES FIG. 1A is a cross-sectional view of an arrangement for growing a layer of Ga In, ,P through the solidliquid-solid procedure of the prior art. It illustrates the evolution of a layer of a ternary compound from a melted zone which has been established in equilibrium originating at the In? layer. A temperature gradient is established at the interface at the lower GaP layer and thereafter the ternary compound is obtained by precipitation from the liquid zone.

FIG. 1B is a pseudo-binary phase diagram for the GaP-InP system. It shows a liquidus and solidus line and the relationships of the tie lines which are a function of various temperatures. The tie lines intercept the liquidus and solidus which are the equilibrium concentrations of the GaP-InP system.

FIG. 1C is a ternary phase diagram of the system Ga--InP. This diagram shows the relationships of the various liquidus lines to their respective solid constituents on the solidus via tie lines. It also shows the relationships of various liquidus concentrations at different pressures and temperatures to the equilibrium solid compositions.

FIG. 2A is a block diagram illustrating schematically the steps of the chemical vapor deposition procedure utilized for the practice of this invention for obtaining a sandwich structure of GaPlnPGaP.

FIG. 2B is a cross-sectional view of the resultant sandwich structure grown by the steps of the procedure illustrated in FIG. ZA showing the substrate holder for the seed crystal and the resultant sandwich structure.

FIG. 2C presents a diagram of an apparatus partially in section for growing a sandwich structure for the practice of this invention by the chemical vapor deposition procedure and for growing a layer of Ga In ,P by the solid-liquid-solid procedure. The various gases and constituent sources for the ehcmical vapor deposition procedure are illustrated. The support substrate for the sandwich structure and the means for establishing a temperature gradient within the reactor chamber are also illustrated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Solid-Liquid-Solid Crystal Growth Procedure In the noted copending patent application Ser. No. 860,316, now US. Pat. No. 3,628,998, a technology is presented for growth of a mixed crystal with controlled composition which is designated herein as the solidliquid-solid process which as an acronym is designated SLS. It is the only available method for growing ternary compounds such as Ga In P with constant mole fraction x. The method is designated herein as a solidliquid-solid procedure and is applicable to ternary compounds that have one component which is volatile.

FIG. 1A shows an arrangement for growing a mixed crystal of Ga In P from a charge 1, according to the principles of the noted copending application Serial No. 60,3l6, now US. No. 3,628,998, consisting of upper and lower layers 2 and 3 of Ga? between which there is sandwiched intermediate layer 4 of InP. An upper solid-liquid interface 5 and a lower solid-liquid interface 6, respectively, are established between the layers 2 and 4 and between the layers 4 and 3. Charge 1 is established in boron nitride crucible 7 which is established in sealed quartz ampoule 8 in vacuum.

For the GaP-InP-GaP charge 1, it is necessary, for single crystal growth, that the liquid phase be at stoichiometry, the phosphorus pressure in the system must be equal to or greater than the phosphorus dissociation pressure of the melt. This can be accomplished by the addition of excess phosphorus 9 in the bottom of quartz ampoule 8. Alternatively, a conventional two-zone furnace, not shown, can be used with condensed phosphorus at the cool end thereof. The temperature of the condensed phosphorus is controlled to achieve the desired pressure in the system. Because of the overpressure of phosphorus 9, quartz ampoule 8 is established in stronger graphite container 1 l which has main shell 12 and screw cap 13. Graphite container 11 is supported by rod 14 held by mechanism 15 for raising and lowering the assembly or ensemble 16 consisting of the graphite container 11 and its contents. Furnace tube 10 has upper heating windings 18 and lower heating windings 20 for establishing the temperature profile 21 with upper and lower isothermal zones 22 and 23 between which there is temperature differential or kink 24. Windings 18 and 20 are energized by power source 19. It has been determined for the practice of the prior art solid-liquid-solid procedure that rates of growth of 0.1 to 0.5 cm per day are obtainable for growth of single crystals of Ga ln of the mixed crystal system 1 GaInP. A suitable rate of growth is readily determined experimentally for the practice thereof and is generally approximately inversely proportional to the equilibrium temperature of the liquid solution.

The InP layer 4 melts when the isothermal temperature 22 is higher than the melting point thereof and dissolves some of the Ga? from both layers 2 and 3. The maximum solubility is determined by the temperature 22 selected. A solid phase appears which is the equilibrium solid phase at the temperature T. This solid phase will be at both upper and lower liquid-solid interfaces 5 and 6. The lower solid layer 3 of Ga? of the composite or charge 1 is now cooled by lowering the assembly 16 through the temperature kink 24, and a solid solution of constant composition precipitates or grows from the liquid at the expense of the upper solid layer 2 of GaP.

The salient features of the SLS process are as follows with reference to FIG. 1A: a sandwich structure comprised of a layer of gallium phosphide 3 which is in contact with a layer of indium phosphide 4 on top of which is another layer of gallium phosphide 2. This sandwich structure is put into a crucible 7 and is maintained at some temperature 22 greater than the melting point of the lowest melting component of this structure, i.e., l070C for InP. In general, for materials which decompose at their melting point, a partial pressure of the volatile constituent is necessary to prevent volatilization and subsequent decomposition of the compound semiconductor. This is accomplished in the normal SLS process by putting sufficient phosphorus within the reaction vessel so that an equilibrium partial pressure-is obtained at the operational temperatures. The sandwich may also be put into a very tightly fitting crucible within a quartz container and the free volume minimized within the container so that the partial pressure of the volatile component within this container is governed by the ideal gas law relationships. In order to describe the process more fully, reference is made to FIG. 1B wherein the composition of a pseudo-binary phase diagram for InP-GaP is given as a function of the temperature T. The left-most component is GaP 36 and the right-most component is In? 38. There is a complete range of mutual solubility as indicated by the liquidus line 32 and solidus line 34, between the melting point temperature T, of Ga? and the melting point temperature T of InP. These lines are the equilibrium lines which separate the respective phase fields for the Ga ln P ternary alloy system. Above the liquidus line 32, all that is present for any composition of InP and GaP is a liquid 30. Below the solidus line 34 for any composition InP and GaP, the resulting phase field is solid. Between the solid 34 and the liquidus 32, the resulting phase field is a mixture of the solid and liquid. For a particular temperature T greater than the melting point T of InP, InP dissolves GaP to the extent dictated by tie line 40 which intersects the liquidus line at point 42 and the solidus line at point 44. Point 42 on the liquidus line 32 is the composition Ll of the equilibrium liquid. Point 44 on the solidius line is the composition S1 of the equilibrium solid. For another temperature T lower than temperature T, but greater than the melting point T of MP, the liquid composition of L2 and the solid composition is S2. The liquid composition and solid composition are determined by the temperature T and also by a pressure variable P. In general, the pressure in the system has been fixed.

Reference to FIG. 1C shows the effect of various pressures on the change of the liquidus line as a function of temperature. FIG. 1C is a ternary phase plot of the system Ga,In, ,P. The lower left hand corner of the equilateral triangle is In 54. The right hand corner is Ga 56. Line 62 joins In 54 to Ga 56. The apex of the triangle is phosphorus 52. At the mid-point of the In? leg 60 is the binary compound InP 66. At the mid-point of the GaP leg 58 is the binary compound GaP 64. Connecting the In? to the Ga? is solidus line 68. The line InP to GaP can be thought of as rotating the pseudobinary phase diagram of FIG. 13 through an angle of 90 coming away from a vertical plane and inserting it into the ternary phase diagram of FIG. 1C. Thus, at stoichiometry, the In? to GaP line in FIG. 1C represents the superposition of the liquidus and solidus lines. This is represented in FIG. 1C as the line joining the InP and GaP. This condition corresponds to the case of a stoichiometric liquid from which a stoichiometric solid as depicted in the pseudo-binary diagram is grown, i.e., there is a unique temperature, a unique liquid composition and a unique solid composition. Once these conditions are fulfilled, the transformation from liquid phase to solid phase can be accomplished without violation of the phase rule relationships.

The phase rule requires that the variance of a system F is equal to the number of components of the system minus the number of phases in equilibrium plus 2. Thus, for the system of this invention where zero variance is desired, i.e., an equilibrium situation such that a stoichiometric solid can be grown from a stoichiometric liquid, there are required a specified temperature, a specified pressure of the volatile components and an equilibrium between solid, liquid and vapor phases. However, if one of the variables, e.g., the pressure P, is not completely determined, then the system shifts to offset or to compensate for the nomequilibrium conditions present. The system tends to adjust itself by shifting the liquidus composition to values which tend to distort the stoichiometry of the liquid phase. If the phosphorus component does not have the equilibrium partial pressure necessary to prevent decomposition, the liquidus shifts to lower temperatures since there is insufficient phosphorus within the reaction vessel to keep the liquidus at the equilibrium pseudo-binary liquidus. Thus the liquidus is shown in FIG. 1C as moving from the equilibrium liquidus 69 to new values of the equilibrium liquidus such as 70, 71, 72, etc.

The temperatures corresponding to these new equilibrium liquidus lines are lower than the temperature necessary for equilibrium liquidus 69. For liquidus 70 there is a temperature T-70, for liquidus 71 there is a temperature T-71, for liquidus 72 there is a temperature T-72. The temperature T--69 is greater than T 70 which is in turn greater than T-71 which is in turn greater than T-72 which is in turn greater than T-73 which is in turn greater than T-74. For liquidus line 70, there is a tie line 81 which connects a point on the solidus with a point 86 on the liquidus 70, and the point 80 is similarly connected to the point 87 on the liquidus 71 by tie line 82and to the point 88 on liquidus 72 by tieline 83, etc.

These tie lines are analogous to the tie lines that were described earlier for the operation of the pseudo-binary phase diagram of FIG. 1B. That is, they connect a liquid with a solid at some temperature T. Referring to FIG. 1A, the operation of the SLS process requires that an equilibrium be established at interface 5 which is the equilibrium solid at that temperature and is depicted by point 80 on tie line 81 of FIG. 1C. The composition of the liquid in equilibrium with that interface is depicted by point 86 on liquidus 70. At the second solid-liquid interface 6 there is again established solid composition 80. If now a temperature gradient is imposed at solidliquid interface 6 of FIG. 1A, the liquid will tend to react to this driving force by depositing solid of composition 80 from the liquid. Thus, the liquid becomes depleted of the higher melting component 2. Since this process is a near equilibrium process the liquid tends to dissolve sufficient solid of composition 3 to again restore it to the equilibrium conditions. Thus, this process is a regenerative one in that as solid of composition 80 is withdrawn from the melt, the melt compensates for the loss of the solid by dissolving additional material to maintain the system in equilibrium.

The ingots which are necessary for use in this prior art solid-liquid-solid process are usually polycrystalline and are usually contaminated with impurities present during original high temperature growth process. These ingots are cut to exact dimensions which increases the possibility of contamination and residual contaminants being left on the surfaces of the Ga? and In? ingots. Therefore, by the time the SL8 process is normally initiated, the starting materials are impure and are polycrystalline. A condition necessary for SLS growth is that Ga? and In? as shown in the sandwich structure in FIG. 1A be in good metallurgical contact, i.e., the surface between the InP and GaP must be one in which a metallurgical bond has taken place. Presence of residual contaminants and spurious nucleation inhibits favorable growth of the ternary alloy Ga ln P. The periods necessary to grow the initial starting materials for the SL8 process and the subsequent SLS process itself are relatively long according to the requirements of the semiconductor device industry. This indicates that the prior SLS process may have some economic limitations for a commercial production level of semiconductor devices.

The apparent limitations of the solid-liquid-solid process as heretofore practiced are obviated by the practice of this invention incorporating a chemical vapor deposition procedure. Accordingly, a special sandwich structure in accordance with the principles hereof is fabricated by chemical vapor deposition prior to growing a desirable layer of ternary compound according to the general principles of the solid-liquid-solid procedure.

A layer grown by solid-liquid-solid crystal growth procedure may also be a stoichiometric line compound rather than a solid solution. When'the layer grown by solid-liquid-solid crystal growth procedure is a solidsolution, the middle layer grown by chemical vapor deposition may be a mixture of two binary compounds rather than a single binary compound.

Chemical Vapor Deposition Procedure The procedure for chemical vapor deposition is illustrated as a block diagram in FIG. 2A, the resultant sandwich is shown in FIG. 2B, and the apparatus and technology for growing the sandwich of FIG. 2B is illustrated in FIG. 2C.

FIG. 2A shows in essence a block diagram 100 of the technique used herein with chemical vapor deposition. A substrate single crystal 102 is placed within a reaction vessel as depicted in FIG. 2C. This substrate single crystal may be GaP or it may be any one of several other commonly used substrates for chemical vapor deposition of GaP. Thus, GaAs, alumina or magnesia are also suitable for use as substrate materials. The first layer GaP 104 is grown by the process of chemical vapor deposition. The conditions necessary for the growth of the second layer by chemical vapor deposition are imposed. The second layer 106 of In? is then grown by chemical vapor deposition. When sufficient material has been deposited, the process is halted and the conditions are again readjusted so that the third layer 108 of GaP can be grown. The sandwich structure 110 that is grown within the reaction vessel is shown diagrammatically in FIG. 2B. Substrate 102 is shown in this schematic diagram which meets GaP layer 104 at interface 105. The first layer 104 of Ga? which is a thin layer approximately 2 mils thick is in metallurgical contact with a second or middle layer In? 106 which joins the GaP layer at interface 107. The middle layer is approximately more of the order of 2 mils thick and is in metallurgical contact with a third layer 108 of Ga? which meets it at interface 109. This third layer also is approximately of the dimension of 2 mils in thickness.

The sandwich structure of FIG. 2B is merely exemplary of the types of structures which are formable by the chemical vapor deposition technique portion of the practice of this invention. Although the exemplary layers are indicated in FIG. 2B as 2 mils thickness, actually such layers can be of several hundred Angstrom units thickness or several millimeters. An illustrative prior art copending application Ser. No. 96,206 for Vapor Phase Epitaxial Deposition Process For Forming Superlattice Structure, filed Dec. 8, 1970, now U.S. Pat. No. 3,721,583, and commonly assigned, is applicable for the chemical vapor deposition portion of this invention.

the sandwich structure 100 of FIG. 2B is very pure since the chemical vapor deposition (CVD) process is inherently a technique for obtaining a pure material; and the layers grown are in metallurgical contact with one another. This reduces the possibility of stray nucleation sites or nucleation centers at the physical boundary or interface between adjoining layers. Such criterion is necessary for single crystal growth of the ternary alloys; i.e., the presence of a single crystal onto which another single crystal can be grown. Although very thin layers of binary compounds can be prepared by chemical vapor deposition, it is generally not possible to prepare homogeneous large area ternary compounds, e.g., Ga,In, ,P, by the same technique. The conditions necessary for the deposition of Ga? and In? are considerably different. In order to grow a ternary alloy by chemical vapor deposition, the conditions must be worked out such that the resulting solid grown from the vapor phase is of desired composition. For the case of Ga Inthe conditions necessary for codeposition are difficult to achieve. At the temperature where the Ga? would deposit, InP has not yet formed and little lnP is deposited with the GaP. At temperatures necessary for crystallization of the In? from the vapor phase, the conditions are such that the GaP has already deposited at a higher temperature and is not crystallized at the same rate as the hi. Chemical Vapor Deposition Apparatus The apparatus for carrying out the chemical vapor deposition procedure of this invention is illustrated in FIG. 2C and consists generally of three essential portions. One portion is a furnace environment for establishing appropriate temperature and temperature gradients for film growth; another portion provides for metal sources to establish a film layer growth environment for the sandwich structure for the practice of this invention; and the other portion involves the gas sources which contribute to the growth process for the sandwich structure.

The furnace assembly includes tubular furnace portions 152A and 152B with heater windings 153A and 153B, respectively. The temperature of the furnace chamber 154 and the gradients within the furnace are controlled by external power sources 156A and 15613. The furnace assembly actually consists of two furnaces. Each furnace has its own external power supply. The high temperature furnace on the left is used for the controlling of the source material temperature and the low temperature furnace on the right is used for control of the substrate temperature. Inside of the tubular furnace on the left is a large diameter quartz reactor 157 which fits within the furnace tube. The left end of the quartz reactor is the high temperature source end. In the source end of the reactor there are dual source tubes 162 and 164 composed of quartz. The two source tubes are joined at the exhaust end into one common tube 165. Source tube 162 contains a quartz boat 166 which contains Ga metal. The other source tube 164 contains a quartz boat 167 which contains In metal. The dual source tube may rest at the bottom of the quartz reactor 157 and is snugly fit to the left end of the reactor by compression of fiber glass. Quartz tubes 170 and 172 feed into the upstream end of each of the source tubes 162 and 164, respectively. A third quartz tube 173 enters at the top of the reactor 157 and terminates at about the middle of the reactor 157. The third quartz tube is a source of phosphine gas. The sources of the gases for the growth procedure will be described later after the description is presented for the portion of the apparatus to the right.

At the right end of the apparatus is the substrate holder 180 which consists of a hollow quartz disc. The substrate holder 180 is attached to a quartz tubing 181 which serves as the substrate holder support and a thermocouple well and also serves as a source of air for cooling in the growth of ternary compound by solidliquid-solid process. The reactor tube 157 terminates in a ground glass joint 182 at the right end of the apparatus via glass coupling 183. The substrate holder tubing 181 exists through the cap 184 connected to the ground glass coupling. The connector can be loosened or tightened to allow movement of the substrate holder support rod. An exhaust tube 185 permits exit of the expended gases in reactor 157.

On top of the quartz substrate holder is a seed crystal 102. Thereon are the layers 104 and, 106 and 108 shown in phantom whose growth will be described later in greater detail. Numeral 100 identifies in FIG. 2C the same sandwich structure as is identified thereby in FIG. 2B.

At the left end of the tube 172, is a phosphorus trichloride bubbler assembly 200A. Phosphorus trichloride is designated PCl The description of assembly 200A begins with a hydrogen tank 202A. Tubing 204A exists from the hydrogen tank and splits into tubes 206A and 208A. Tube 206A goes via stop-cock 207A through a flow meter 210A and exits from the flow meter as tube 212A. Tube 208A goes via stop-cock 209A through a second flow meter 214A and exits from the flow meter as tube 216A. Tube 216A feeds directly to the phosphorus trichloride bubbler 218A. Bubbler 218A sets in a coolant 223A which is in a vacuum wall liquid container 224A. Tube 216A splits into tube 220A and tube 222A. Tube 220A goes into the phosphorus trichloride bubbler 218A. Tube 204A contains a stop-cock 225A. When the stopcock 225A is open, hydrogen gas flows directly through tube 216A and carries no PC13. When stop-cock 225A is closed, the hydrogen gas is diverted through tube 220A into the PCI bubbler and carries the PC];, vapor out of the bubbler through tube 222A. The PG; vapor then enters the reactor tube 157 through tube 172. Tube 212A serves really as a hydrogen diluent tube. Hydrogen diluent flow and H flow through PC];, can be controlled via stop-cocks 207A and 209A.

There is an identical system for introducing hydrogen and PCl into tube 170 whose numbers are the same as we have just described except with appended B designation instead of appended A designation.

The source of the phosphine gas will now be described. The source of phosphine for the SL5 growth consists of a phosphine tank 230. The phosphine tank feeds into tube 232 through stop-cock 233 then into flow meter 234 and then into tube 173.

Practice of the Invention The growth of a three layer sandwich structure composed of GaP, InP and GaP will now be described. A seed crystal is placed on the quartz substrate holder 180. The first layer to be grown is GaP. The temperatures for growth of the Ga? is a 900C Ga source and an 800C seed temperature. To begin the GaP vapor growth, 50 cubic centimeters per minute of hydrogen is passed from source 202B through the PCI;, bubbler 218B and 50 cubic centimeters per minute of hydrogen diluent is also introduced into the system via tube 170 from source 202B. The 50 cubic centrimeters per minute of hydrogen is saturated with PCl in the bubbler and passes over the 900C Ga source. The PC];, is decomposed into phosphorus and chlorine and the chlorine gas transports the Ga metal as GaCl vapor via tube into reactor 157. When the GaCl vapor reaches the seed crystal 102 at a temperature of 800C, it disproportionates into Ga metal vapor which then recombines with the phosphorus vapor resulting in the formation of GaP single crystal 104. After the GaP growth is finished, the source temperature is lowered to 800C and the substrate 102 temperature to 675C. PC] vapor is then introduced into the indium source tube 172 from source 218A in the same manner as into the Ga source tube for the prior growth. The same flow rates of hydrogen and PC];, are used in the lnP growth as was used in the GaP growth. Indium chloride is produced by reaction of the In with the chlorine vapor and in the same manner as with the GaP, the indium chloride vapor disproportionates at the substrate position into indium metal which then recombines with the phosphorus to form an indium phosphide (lnP) layer. When the InP growth is terminated, the temperatures are readjusted to the initial GaP growth temperatures, i.e., a source temperature of 900C and a substrate temperature of 800C. The procedure for growth of GaP films is then repeated. When the growth of the second layer 108 of GaP is terminated, the PC1 flow is also stopped.

The special concerns in the growth procedure will now be discussed, i.e., the critical parameters and the ones which need not be so critically adjusted. The most critical factors are the flow rates so that uniform growth may be obtained with suitable growth rate. The temperature of the substrate is critical for growth of smooth uniform single crystals. The temperature of the source materials is less critical, the transport rate of Ga and In in the temperature range of concern are not as dependent on temperature as the perfection of the film is dependent on substrate temperature. All growth parameters are under control and growth rate may be either increased or decreased by control of the flow rate of the input gases and somewhat by control of substrate temperature. However, the substrate temperature is usually not varied during growth of the sandwich structure 100 since it can affect the perfection of the grown single crystal film.

The chemical formulae that describe the growth procedure hereof are readily determined from the formulae presented in the paper by R. Taylor in the J. Elec. Chem. Soc., April 1967, which provides the appropriate formulae for the growth procedure for GaAs by chemical vapor deposition.

With reference to FIG. 2C, the SL8 procedure is accomplished by heating the sandwich 100 in an appropriate temperature gradient by injecting cool air at the lower face of the substrate 102 via tube 181 to provide the temperature gradient. Alternatively, the entire assembly of substrate 180 with pipe 181 and sandwich structure 100 may be removed from chamber 154 and the solid-liquid-solid growth procedure of a layer of Ga ln, P be carried out externally. The SLS growth procedure is accomplished externally of chamber 154 in accordance with the apparatus and procedure described hereinbefore with reference to FIG. 1A.

What is claimed is:

1. Method for growing a region ofa multicomponent compound of a mixed crystal system with more than two components selected from the homologous group of mixed IlI-III-V arsenides, phosphides and antimonides, comprising the steps of:

growing a sandwich structure by chemical vapor deposition procedure including the steps of establishing a crystalline substrate for growth of a sandwich structure at a given location,

establishing appropriate material sources and gas sources for growing a plurality of layers of constituent components of said multicomponent compound by chemical reactions at said given location in a reaction chamber,

whereby said sandwich structure is established at said given location having first, second, and third solid thin film layers, 1

said first and third layers being of one component of said mixed crystal system,

said second layer being of another component of said mixed crystal system, said second layer being intermediate to said first and third layers, and having lower melting point; and

growing a region of said multicomponent compound by solid-liquid-solid crystal growth procedure including the steps of establishing a substantially equilibrium condition of said sandwich structure at a temperature above the melting point of said intermediate layer and below the melting point of said first and third layers to obtain a liquid zone with a given composition with first and second liquid-solid-interfaces in said second and third layers,

lowering the temperature at one said solid-liquid interface between said intermediate liquid zone and one said adjacent solid layer, and

growing said crystalline region at said latter liquidsolid interface.

2. Method as set forth in claim 1 wherein said group of selected arsenides, phosphides and antimonides comprises: Ga ln P, Ga In As, Ga,In ,Sb, In AI- ,.P, In Al As, and In,Al, ,Sb.

3. Method of growing a region of a multicomponent compound of the mixed crystal system Ga In ,P comprising the steps of:

growing a sandwich structure at a given location having first, second, and third solid thin film layers, said first layer being of one component 0a? of said mixed crystal system,

said second layer being of another component In? of said mixed crystal system,

said third layer being of said one component GaP of said mixed crystal system,

said second layer being intermediate to said first and third layers, and having lower melting point;

said growing of said sandwich structure including the steps of establishing a crystalline substrate in a first given temperature region,

establishing first Ga and second In source materials in another given temperature region; establishing first H and second PCl gas sources respectively for obtaining respective volatile compounds of said corresponding source materials by first and second chemical reactions therewith,

transporting said volatile compound of said first source material to the surface of said substrate where said source material is deposited thereat by third chemical reaction,

establishing a vapor of another component of said first layer to be grown at the substrate, whereby said first layer is grown at said substrate by fourth chemical reaction between said first source material thereat and said vapor,

transporting said other volatile compound of said second source material to said first grown layer and growing thereat said second layer by fifth chemical reaction between said second source material deposited at said first layer by sixth chemical reaction from said second volatile compound and said vapor, and

growing said third layer thereof of said sandwich structure by seventh chemical reaction between said vapor and said first source material obtained by eighth chemical reaction of said first volatile compound at said second layer; and

growing a region of said multicomponent compound from said sandwich structure by solid-liquid-solid procedure including the steps of establishing a substantially equilibrium condition of said sandwich structure at a temperature above the melting point of said intermediate layer and below the melting point of said second and third layers to obtain a liquid zone with a given composition with first and second liquid-solid-interfaces at said second and third layers,

lowering the temperature at one said solid-liquid interface between said intermediate liquid zone and one said adjacent solid layer, and

growing said crystalline region at said latter liquidsolid interface.

4. A method as set forth in claim 3 wherein said third and fifth chemical reactions are disproportionation reactions.

5. Method for growing a region of the multicomponent compound of a mixed crystal system with more than two components AlP ,As comprising the steps of:

growing a sandwich structure by chemical vapor deposition procedure including the steps of establishing a crystalline substrate for growth of a sandwich structure at a given location,

establishing appropriate material sources and gas sources for growing a plurality of layers of constituent components of said multicomponent compound by chemical reactions'at said given location in a reaction chamber,

whereby said sandwich structure is established at said given location having first, second, and third solid thin film layers,

said first and third layers being of one component of said mixed crystal system,

said second layer being of another component of said mixed crystal system,

said second layer being intermediate to said first and third layers, and having lower melting point; and

growing a region of said multicomponent compound by solid-liquid-solid crystal growth procedure including the steps of establishing a substantially equilibrium condition of said sandwich structure at a temperature above the melting point of said intermediate layer and below the melting point of said first and third layers to obtain a liquid zone with a given composition with first and second liquid-solid-interfaces in said second and third layers,

lowering the temperature at one said solid-liquid interface between said intermediate liquid zone and one said adjacent solid layer, and

growing said crystalline region at said latter liquidsolid interface. 

2. Method as set forth in claim 1 wherein said group of selected arsenides, phosphides and antimonides comprises: GaxIn1 xP, GaxIn1 xAs, GaxIn1 xSb, InxAl1 xP, InxAl1 xAs, and InxAl1 xSb.
 3. Method of growing a region of a multicomponent compound of the mixed crystal system GaxIn1 xP comprising the steps of: growing a sandwich structure at a given location having first, second, and third solid thin film layers, said first layer being of one component GaP of said mixed crystal system, said second layer being of another component InP of said mixed crystal system, said third layer being of said one component GaP of said mixed crystal system, said second layer being intermediate to said first and third layers, and having lower melting point; said growing of said sandwich structure including the steps of establishing a crystalline substrate in a first given temperature region, establishing first Ga and second In source materials in another given temperature region; establishing first H2 and second PCl3 gas sources respectively for obtaining respective volatile compounds of said corresponding source materials by first and second chemical reactions therewith, transporting said volatile compound of said first source material to the surface of said substrate where said source material is deposited thereat by third chemical reaction, establishing a vapor of another component of said first layer to be grown at the substrate, whereby said first layer is grown at said substrate by fourth chemical reaction between said first source material thereat and said vapor, transporting said other volatile compound of said second source material to said first grown layer and growing thereat said second layer by fifth chemical reaction between said second source material deposited at said first layer by sixth chemical reaction from said second volatile compound and said vapor, and growing said third layer thereof of said sandwich structure by seventh chemical reaction between said vapor and said first source material obtained by eighth chemical reaction of said first volatile compound at said second layer; and growing a region of said multicomponent compound from said sandwich structure by solid-liquid-solid procedure including the steps of establishing a substantially equilibrium condition of said sandwich structure at a temperature above the melting point of said intermediate layer and below the melting point of said second and third layers to obtain a liquid zone with a given composition with first and second liquid-solid-interfaces at said second and third layers, lowering the temperature at one said solid-liquid interface between said intermediate liquid zone and one said adjacent solid layer, and growing said crystalline region at said latter liquid-solid interface.
 4. A method as set forth in claim 3 wherein said third and fifth chemical reactions are disproportionation reactions.
 5. Method for growing a region of the multicomponent compound of a mixed crystal system with more than two components AlP1 xAs x, comprising the steps of: growing a sandwich structure by chemical vapor deposition procedure including the steps of establishing a crystalline substrate for growth of a sandwich structure at a given location, establishing appropriate material sources and gas sources for growing a plurality of layers of constituent components of said multicomponent compound by chemical reactions at said given location in a reaction chamber, whereby said sandwich structure is established at said given location having first, second, and third solid thin film layers, said first and third layers being of one component of said mixed crystal system, said second layer being of another component of said mixed crystal system, said second layer being intermediate to said first and third layers, and having lower melting point; and growing a region of said multicomponent compound by solid-liquid-solid crystal growth procedure including the steps of establishing a substantially equilibrium condition of said sandwich structure at a temperature above the melting point of said intermediate layer and below the melting point of said first and third layers to obtain a liquid zone with a given composition with first and second liquid-solid-interfaces in said second and third layers, lowering the temperature at one said solid-liquid interface between said intermediate liquid zone and one said adjacent solid layer, and growing said crystalline region at said latter liquid-solid interface. 